Analyzing structural design relative to vibrational and/or acoustic loading

ABSTRACT

A computer-performed method of designing a structure. User-selected design parameters are input to a parametric model of the structure. Boundary conditions and load conditions are applied to the model to determine a response of the structure to the conditions. Based on the load conditions, an analysis method is selected. The modeled response is analyzed using the selected analysis method to obtain power spectral density (PSD) values for the model. The PSD values are averaged over a user-selected frequency range to evaluate the design parameters for acoustic transmission loss. This method provides a high degree of flexibility in formulating structural design analyses.

FIELD

The present disclosure relates generally to designing structures andmore particularly (but not exclusively) to analyzing responses of astructural model to optimize a structural design.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Commercial aircraft are expected to withstand a wide range of pressureconditions and turbulence during flight. Evaluation of design conceptsfor structures subjected to such conditions typically has involvedlengthy and complex analysis and testing procedures.

SUMMARY

In one implementation, the disclosure is directed to acomputer-performed method of designing a structure. One or moreuser-selected design parameters are received. The design parameters areinput to a parametric model of the structure. One or more boundaryconditions and one or more load conditions are applied to the model tosimulate a response of the structure to the conditions. Based on atleast one of the load conditions, an analysis method is selected. Thesimulated response is analyzed using the selected analysis method toobtain one or more power spectral density (PSD) values for the model.The PSD values are averaged over a user-selected frequency range toevaluate the design parameters.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples, while indicating various preferred embodiments of thedisclosure, are intended for purposes of illustration only and are notintended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a flow diagram of a method of designing a structure inaccordance with one implementation of the disclosure;

FIG. 2 illustrates a group of screen shots of mode shapes of fourpressurized modes of the belt model response in accordance with oneimplementation of the disclosure; and

FIG. 3 is graph of average broadband velocity PSD for four window typesin accordance with one implementation of the disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no wayintended to limit the present disclosure, application, or uses.

The present disclosure, in some implementations, is directed to a systemand methods for analyzing structural finite element models underaero-acoustic loading with pressure and/or thermal preloading. Althoughvarious implementations of the disclosure are described with referenceto aircraft and panel structures in aircraft, the disclosure is not solimited. The disclosure may be implemented in connection with variouskinds of structures and in various environments.

The present disclosure, in some implementations, is directed to acomputer-performed method of designing a structure, e.g., a panel orother structure of an aircraft. In one implementation, a computerreceives one or more user-selected design parameters. The designparameters are input to a parametric model of the structure. Thecomputer applies one or more boundary conditions and one or more loadconditions to the model to calculate response of the structure to theconditions. Based on at least one of the load conditions, the computerselects an analysis method. The computer uses the selected analysismethod to analyze the modeled response, to obtain one or more powerspectral density (PSD) values for the model. The computer averages thePSD values over a user-selected frequency range to evaluate the designparameters. If the design parameters are not yet optimized, the computermay adjust the design parameters and repeat the foregoing method untilthe design parameters are optimized.

An exemplary implementation of a method of designing a structure isindicated generally in FIG. 1 by reference number 120. The method 120may be performed by one or more computer, indicated conceptually byreference number 124, having one or more processors and memory. It maybe desirable in some cases for the method 120 to be implemented on morethan one computer, for example, in a distributed queuing environment.For the sake of simplicity, however, the present disclosure shall referto only one computer 124. A user interface (not shown), e.g., a monitor,laptop or other display capability in communication with the computer124, may be used to receive user input and to display results of themethod 120.

In the present example, the method 120 is used to optimize a design fora window panel for an aircraft. The method 120 is commenced in block128. In block 130, the computer 124 receives one or more user-selecteddesign parameters. Such parameters may specify, e.g., window shape(s),layup(s), material(s), effect(s) of vacuum and/or viscous materialeffect(s).

The design parameters are input to a parametric model of the windowpanel structure in block 134. The model includes nodes and elements,e.g., brick and/or shell elements, describing geometry of the structure,e.g., in a format compatible with NIKE3D, a known three-dimensionalfinite element tool. It should be noted, however, that the disclosurecould be implemented in connection with finite element tools other thanNIKE3D, for example, NASTRAN, ANSYS, or ABAQUS. The model also includesone or more pressure boundary conditions specifying elements of acousticload to be applied during model simulation.

A power spectrum density (PSD) output list is input by the user in block138 to the computer 124. The PSD output list is used to indicate modelelements for which stress PSDs are to be computed as further describedbelow. The PSD output list also includes model nodes for whichdisplacement, velocity and/or acceleration PSDs are to be computed. Ifaverage value over an area such a window pane is needed, a file namethat specifies the area of interest may be specified instead of nodes orelements. The PSD output list also may include a frequency range overwhich an average PSD is to be calculated, e.g., for implementations inwhich it may not be desirable or feasible to calculate a PSD averageover a full spectrum.

An environment file is input by the user in block 142 to the computer124. The environment file includes data descriptive of an environment inwhich the model is to be simulated. The environment file may includedata specifying one or more of a plurality of load conditions that maybe user-selected for application to the model. Such load conditions mayinclude, for example, a progressive wave, a reverberant wave, aturbulent boundary layer, a base excitation, a plane wave, and/or apoint load.

The environment file also includes a flag indicating which of the loadconditions is selected for application to the model. Structural dampinginformation may also be included in the environment file. In block 146the computer 124 formats data in the parametric model, the output listand the environment file into a NIKE3D input deck for eigensolution. Inblock 150, the input deck from block 146 is input to NIKE3D.

It may be desirable to preload the model with initial stress data, e.g.,initial thermal and/or pressure conditions. Initial condition data mayinclude, for example, a TOPAZ plotfile of thermal data. TOPAZ ismaintained by Lawrence Livermore National Laboratory. Accordingly, inblock 154 it is determined whether preloading is to be performed. Ifyes, then in block 158 pressure preload data and/or thermal preload dataare input and processed to obtain a NIKE3D input deck in block 162. Thepreload input deck also is input to NIKE3D in block 150.

In block 150, NIKE3D is executed to simulate the model. NIKE3D extractseigenvalues and eigenvectors representing frequencies and mode shapes ofthe structure. A mass matrix also is extracted. In block 166, the dataextracted in block 150 is used to obtain data representative of jointacceptance between the structure model and the applied loadcondition(s).

In block 170 the previously mentioned flag of the environment file istested to determine which load condition is being applied to the model.Dependent on load condition type, in block 174 the computer 124 mayperform one of a plurality of analysis methods. For example, for soundpressure level PSDs (where the load condition is, e.g., a progressivewave, a reverberant wave or a turbulent boundary layer), a modesuperposition method is performed. For acceleration PSDs, pressure PSDsor nodal force PSDs, a mode acceleration method is performed in block174. Where mode superposition is performed relative to an appropriateload condition, the load condition is supplied to block 166 for use incalculating joint acceptance data.

In block 174 the computer 124 assembles the frequencies, mode shapes andmass matrix from block 150 and, for appropriate load conditions, jointacceptance data from block 166, to obtain nodal displacement, velocity,acceleration PSDs and/or element stresses in the form of rms(root-mean-square), zero-crossing frequency, and PSD. For baseexcitation, point loading and pressure loading conditions, assembly isstraightforward, following a mode acceleration formulation. For acousticloading conditions, structural behavior is treated by finite elementmodeling (FEM) and acoustic behavior is treated using spatialcorrelation via joint acceptance, which describes the coupling betweenan excitation pressure field and a structure represented by its normalvibration modes. It should be noted that other or additional methods ofanalysis may be performed relative to various types of loading. Forexample, in some implementations, random vibration and/or harmonicvibration may be analyzed.

In block 178, the computer 124 retrieves input from the PSD output list(previously referred to with reference to block 138) for use in block174. File input may specify nodes, files, and/or elements of the modelfor which PSD displacement, velocity and acceleration are to becomputed. If a file is specified, the file includes an area of theresponse and number of grids over which broadband average value iscalculated. Also included in a file may be a frequency range, previouslydiscussed with reference to block 138, over which broadband averagevalue is to be calculated in block 174.

Nodal displacement, velocity, and/or acceleration PSDs from block 174may be displayed in graphic format and are used in block 182 tocalculate and display broadband average PSD for the specified nodesand/or file. Broadband average PSDs also may be displayed in graphicformat.

In block 186, the design parameters are evaluated with reference to theforegoing PSD values and averages. If the design parameters areevaluated as optimal, the method terminates in block 190. If the designparameters are not evaluated as optimal, the computer 124 in block 194performs sensitivity analysis on the parameters, adjusts themaccordingly, and control returns to block 130. Blocks of the method 120may be repeated, for example, until the design parameters converge to anoptimized design for the structure.

In one exemplary implementation of the disclosure, the effect ofboundary conditions on an aircraft window was investigated. A three-baywindow belt finite element model was constructed. An implementation ofthe disclosure was used to perform noise-structural coupling. VelocityPSD was selected as a parameter for evaluating the window performanceunder turbulent boundary layer wave (TBL) as a source of excitation. Themodel was used to evaluate window response in terms of the velocity PSDover an array of nodes on the interior pane. Exemplary mode shapes offour pressurized modes of the belt model response are shown in FIG. 2.Average broadband velocity PSD for a window model may be displayed asshown in FIG. 3. Exemplary results of analyses for four window types areshown in FIG. 3.

The foregoing methods and system make it possible to develop a series ofdesign curves with clear trends that aid in achieving optimal structuraldesigns. A variety of load conditions can be simulated for structuralanalysis, and a variety of model responses can be analyzed. Theforegoing methods and system provide a high degree of flexibility inanalyzing all and/or part of a structural design.

While various preferred embodiments have been described, those skilledin the art will recognize modifications or variations which might bemade without departing from the inventive concept. The examplesillustrate the disclosure and are not intended to limit it. Therefore,the description and claims should be interpreted liberally with onlysuch limitation as is necessary in view of the pertinent prior art.

1. A method of designing a structure, the method comprising: receivingone or more user-selected design parameters; inputting the designparameters to a parametric model of the structure; representing one ormore load conditions as one or more input power spectral density (PSD)values that define one or more excitation conditions, applying one ormore boundary conditions and the one or more input PSD values to themodel to simulate a response of the structure to the one or more loadconditions; based on a type of the one or more input PSD valuesrepresenting at least one of the one or more load conditions, selectinga modal analysis method; analyzing the simulated response using theselected analysis method to obtain power spectral density (PSD) valuesrepresenting nodal displacement, nodal acceleration, nodal velocity, andelement stress for user-selected structural elements of the model;averaging at least some of the obtained PSD values over a user-selectedfrequency range to evaluate effects of excitation-structural coupling onthe structure; and based on the averaged PSD values, adjusting thedesign parameters for convergence toward an optimized design for thestructure; the method performed by one or more processors and memory. 2.The method of claim 1, further comprising: preloading onto the modeldata representing one or more initial stress conditions affecting thestructure; and including effects of the initial stress conditions in thesimulated response.
 3. The method of claim 2, the initial stressconditions comprising at least one of a thermal condition and a pressurecondition.
 4. The method of claim 1, further comprising: based on theselected analysis method, using the simulated response to obtain jointacceptance data and analyzing the simulated response using the jointacceptance data.
 5. The method of claim 1, wherein the one or moreboundary conditions include a pressure boundary condition.
 6. The methodof claim 1, further comprising: receiving from the user a specificationof a portion of the model for which the analyzing and averaging are tobe performed; and performing the analyzing and averaging for thespecified portion.
 7. The method of claim 1, wherein representing one ormore load conditions comprises representing one or more of thefollowing: a progressive wave, a reverberant wave, a turbulent boundarylayer, a base excitation, a plane wave, and a point load.
 8. A method ofoptimizing a design of a structure comprising: inputting one or moredesign parameters selected by a user to a parametric model of thestructure; preloading the model with data representing one or moreinitial stresses on the structure and simulating a response by thestressed structure to the initial stresses; receiving one or moreexcitation conditions specified by the user as one or more input powerspectral density (PSD) values; applying one or more boundary conditionsand one or more of the input PSD values to the model to obtain datadescriptive of a response of the stressed structure to the one or moreexcitation conditions; based on a type of input PSD representing atleast one of the one or more specified excitation conditions, selectingone of a plurality of frequency-domain analysis methods; using theselected analysis method to analyze the data to obtain power spectraldensity (PSD) values representing nodal displacement, nodalacceleration, nodal velocity, and element stress for one or moreselected structural elements of the model; averaging one or more of theobtained PSD values over a user-selected frequency range to evaluateeffects of excitation-structural coupling on the structure; and based onthe averaging of the one or more obtained PSD values: adjusting thedesign parameters; providing the adjusted design parameters to themodel; and repeating at least the applying, selecting, and using stepsto obtain an optimized design; the method performed by one or moreprocessors and memory.
 9. The method of claim 8, further comprisingapplying one or more initial conditions selected by the user to themodel to obtain the data.
 10. The method of claim 8, wherein the dataincludes one or more natural frequencies, one or more mode shapes, and amass matrix.
 11. The method of claim 8, wherein the selected analysismethod includes at least one of mode superposition and modeacceleration.
 12. The method of claim 8, wherein applying an excitationcondition comprises applying one selected from the following: aprogressive wave, a reverberant wave, a turbulent boundary layer, a baseexcitation, a plane wave, and a point load.
 13. The method of claim 8,wherein the one or more initial stresses include at least one of athermal condition and a pressure condition.
 14. A system for designing astructure comprising one or more processors and memory configured to:receive one or more design parameters selected by a user; input thedesign parameters to a parametric model of the structure; represent oneor more excitation conditions specified by the user as one or more inputpower spectral density (PSD) values; apply one or more boundaryconditions and one or more of the input PSD values to the model toobtain frequency-domain data descriptive of a response of the structureto the one or more excitation conditions; based on a type of input PSDrepresenting at least one of the one or more specified excitationconditions, select one of a plurality of modal response analysismethods; use the selected analysis method to analyze the data to obtainpower spectral density (PSD) values representing effects ofexcitation-structural coupling on one or more selected structuralelements of the model; wherein the obtained PSD values comprise at leastone of values representing nodal displacement, nodal acceleration, nodalvelocity and element stress; averaging one or more of the obtained PSDvalues over a user-selected frequency range to evaluate effects ofexcitation-structural coupling on the structure; and based on the one ormore obtained PSD values: adjust the design parameters; provide theadjusted design parameters to the model; and repeat at least theapplying and using to obtain an optimized design.
 15. The system ofclaim 14, wherein the processor is further configured to apply one ormore initial conditions selected by the user to the model to obtain thedata.
 16. The system of claim 14, wherein the data comprises one or morenatural frequencies, one or more mode shapes, and a mass matrix.
 17. Thesystem of claim 14, wherein the response analysis methods comprise modesuperposition and mode acceleration.
 18. The system of claim 14, whereinconfigured to apply an excitation condition comprises configured toapply one selected from the following: a progressive wave, a reverberantwave, a turbulent boundary layer, a base excitation, a plane wave, and apoint load.
 19. The system of claim 14, wherein the processor is furtherconfigured to input data to the model representing initial stressconditions affecting the structure prior to application of the one ormore excitation conditions.